This dictionary says
blow: 2 a : to create a current of moving air by breathing
She blew on her fingers to warm them.
He was blowing on his soup to cool it off.
She blew air into the balloon.
But other dictionary says
blow: 3 AIR FROM YOUR MOUTH [intransitive, transitive always + adverb/preposition] to send air out from your mouth
blow (something) into/onto/out etc
She blew onto her coffee to cool it down.
He blew the smoke right in my face.
So, we say:
She blew on or in his face?